A high aspect ratio light distribution structure is one in which the size of the structure's light emitting area is large compared to a characteristic cross-sectional width of the structure. Such structures commonly have a single localized light source.
Examples of this concept are light guiding systems based on prism light guide material as described in U.S. Pat. Nos. 4,260,220; 4,615,579; and, 4,787,708 (Whitehead); or, metallic light guides as described in U.S. Pat. No. 4,105,293 (Aizenberg et al). Such prior art light guides have predominantly reflective interior surfaces. Accordingly, light rays entering one end of the guide are reflected by the guide's inner walls as the rays proceed to the other end of the guide. Such prior art light guides are designed to "leak" light in a controlled manner, such that the amount of light emitted from the guide per unit length is acceptably uniform along the entire length of the guide.
Although such prior art light guides are very useful for general light distribution purposes, they do not perform well in situations in which it is desirable to have light emitted within a narrowly restricted range of angles from a large light emitting area, while maintaining highly uniform light distribution over the entire light emitting area. Examples of situations in which such characteristics are desirable include linear navigational beacons, which preferably emit maximum light intensity in a substantially horizontal direction; certain backlit liquid crystal displays, which preferably emit light only within a desired range of viewing angles; and, certain vehicle signal lights, which preferably emit maximum light intensity only in desired directions. In each situation it is necessary to efficiently restrict the emitted light to a desired direction, while maintaining highly uniform light distribution over the entire light emitting surface. The present invention satisfies these requirements and thus facilitates the construction of highly directional, highly uniform, high aspect ratio light emitters.